The Conservative Party expelled its largest donor last night after a public row about David Cameron's "say-nothing" policy on Europe.

The spread-betting tycoon Stuart Wheeler, who donated £5m to the Tories in 2001, has given £100,000 to the Eurosceptic UK Independence Party and said he will vote for it in June's European elections because he believes Mr Cameron is failing to represent Britain's interests by stifling internal debate on the EU. Mr Wheeler believes Brussels is a bigger threat to Britain than the global recession. He said yesterday morning that the threat of being kicked out by the Tories did not "alter his stance at all". News of his expulsion broke at 8pm.

Speaking earlier on BBC1's Politics Show, the 74-year-old said: "I think it's very important the Conservatives win the next election but even more important is getting the European Union right. I'm afraid I put that above getting the Conservatives in."

The situation compounds Mr Cameron's headache over his party's European policy. Earlier this month Mr Cameron promised to fulfil a pledge to withdraw his MEPs from the European People's Party – the alliance of mainstream centre-right parties at Brussels – and set up a new grouping in Strasbourg after the elections to oppose closer European union.

But finding savoury bedfellows has proved challenging. One ally, the Czech Civic Democrats, lost power at home last week and its founder is sceptical about climate change. The shadow Foreign Secretary William Hague recently met a leader of the Latvian Fatherland and Freedom Party to discuss an alliance. Party members include nationalists who every year commemorate a Latvian Waffen SS unit.

Mr Wheeler, a close friend of Michael Howard, opposes Mr Cameron's desire to keep the problematic topic of Europe off the party agenda – particularly the matter of a British referendum on the Lisbon Treaty. Last year Mr Wheeler unsuccessfully attempted to sue Gordon Brown over his refusal to hold a referendum, after raising a war chest of over £170,000.

"The Conservatives – though perhaps more Eurosceptic than Labour – just wish no one would talk about the EU so that they can win the general election in peace," Mr Wheeler said, urging Tory voters to vote UKIP at the European elections.